How is the degree of preexcitation on a surface electrocardiogram (ECG) estimated in Wolff-Parkinson-White (WPW) syndrome?

Updated: Jan 08, 2017
  • Author: Christopher R Ellis, MD, FACC, FHRS; Chief Editor: Mikhael F El-Chami, MD  more...
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The degree of preexcitation on a surface ECG in a person with WPW pattern can be estimated by the width of the QRS and the length of the PR interval. A wider or more preexcited QRS with a short PR interval with absent or nearly absent isoelectric component reveals that most (or all) of the ventricular depolarization initiates through the AP insertion rather than through the AV node/His Purkinje system. This would be typical with right free wall pathways where the atrial insertion is close to the sinoatrial (SA) node.

However, the QRS width may vary, becoming narrower during more rapid heart rates. This is possible because catecholamines permit the AV node to contribute more (or entirely) to ventricular depolarization by enhancing AV node conduction; the AV node connects to the entire and usual His-Purkinje system, resulting in the narrow QRS complex.

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